The UCSD Mother-Child-Adolescent HIV Program has been an integral part of the PACTG since pediatric and perinatal clinical trials units were independently funded in 1988. The UCSD PACTU (henceforth referred to as the UCSD Clinical Trials Unit or UCSD CTU) has contributed to all aspects of the perinatal, pediatric and adolescent agenda of the PACTG and proposes in this application to continue its record of outstanding achievement as part of the IMPAACT Network. Investigators from the UCSD CTU have made important contributions to the development, implementation and dissemination of the PACTG research agenda and have held leadership positions critical to the success of the Group. Dr. Spector has chaired the Executive Committee of the PACTG for the past 10 years and will serve as a consultant to the leadership group of the newly formed IMPAACT Network. The outstanding record of accomplishment of the UCSD CTU has been a result of the cooperative efforts of committed clinical investigators and laboratory scientists, dedicated research staff and a highly supportive community. The major contributions of our CTU to the PACTG include providing leadership at the national and international level and contributing expertise in antiretroviral therapy, interruption of perinatal transmission, virology, immunology and vaccine development, pharmacology, opportunistic pathogens and adolescents, and the accrual of significant numbers of patients to clinical trials. UCSD investigators have led numerous protocols, served on a broad range of committees and contributed as members of many protocol teams. In addition to making a full commitment to accrual of study participants, the UCSD CTU has unique expertise that will enable it to make important contributions to the priority areas of research identified by the IMPAACT Network including: interruption of Mother to Child Transmission, Translational Research/Drug Development, Optimization Of Clinical Management Including Co-Morbidities, and Vaccines and Immune Based Therapies. The UCSD CTU has been rated 4th among all sites applying to participate within the IMPAACT Network and has been identified as a "highly preferred site" by IMPAACT.